I am here to tell you that those cards can be both good and bad and that you do not have to be afraid of them. In fact, in my opinion, they can be a frugal fashionista's most useful tool in getting the best bargains. I have had one bad experience but that was a result of my own unwise action.
The key to being responsible with a store cards it to use it like you use cash. Act like it's a debit card. If you don't have the money to pay for whatever you are buying, don't buy it. Think through all your purchases the way you do when you use cash because you will have to pay it back eventually.
This can't be said enough: Read the fine print! Make sure you understand what the APR and rate of interest is. Some of these cards come with great benefits and welcoming discounts but also with high consequences when used irresponsibly.
They can be your wallet's best friends or worst enemies, the cards are in your hands... literally ^_^
Pay off your balances as soon as you can before you forget. I now pay mine online but not through automatic payments (I don't want anyone's grubby little hands in my bank account besides me. but that's just me)
It can be totally worth it if is for a store that you shop in anyway or where you will need to shop for work attire or anything else else you will be required to buy. Also consider the rewards and benefits. If they are not too out of reach, then go for it. My Banana Rep. card gives $10 for $200 I spend. As cheap as I am, that kind of deal doesn't make me want to go running but I thought about it and saw that after some time I will eventually spend that much even if it is over a long period of time. And because I only shop the sales and look for the best deals, I will get a reward for my already frugal habits.
Personal testimony: I got two great quality silk cotton cardigans for $10 each in Banana Republic. They were on sale for $20 each w/ addt'l 40% off = $30 for both + my $10 reward = $20. I got two items which were great additions to my wardrobe in great colors for the season for a price that even H&M cannot compete with.
Funny thing is, I saw a J.Crew cardigan a lot like the one I got for $10 in the same color for like $80 or something (it might have been even more than that but I cannot remember the exact price) in a fashion magazine.
I have also gotten countless matchless deals in Macy's and Victoria's Secret over the years through these cards. I use my mom's Macy's & VS cards because surely, as much we love VS, neither of us shop there enough on our own to earn the benefits, so we work as team and it works out great.
*Disclaimer: To thine own self be true. If you know yourself and know that you cannot be responsible in your shopping then avoid credits cards all cost!
All in all, a store card should reward you for your spending and help you in a future bargain buy instead of drive you into debt by making you spend more than you usually would. Lastly I say, Be responsible and have no fear!